1. Field of the Invention
The present invention relates to an internal electrode for a piezoelectric device having a large effective area, a piezoelectric device including the same, and a method for manufacturing a piezoelectric device.
2. Description of the Related Art
Recently, in mobile electronic devices such as mobile phones, mobile game consoles and e-books, vibrations have been used to silently notify a user of an incoming call as well as to provide a feedback signal to a user in the case of touch input devices.
As a component for generating vibrations, a piezoelectric device having a response speed faster than that of existing vibration motors and operable at various frequencies is being used.
A piezoelectric device is a device using the piezoelectric effect, i.e., an effect in which electrical polarization occurs in response to applied external pressure so that a potential difference occurs, and in reverse, mechanical deformation or mechanical stress is generated in response to voltage applied thereto.
Piezoelectric devices (elements) are manufactured using materials having an excellent degree of piezoelectricity such as crystal, tourmaline, Rochelle salts, barium titanate, monoammonium phosphate or tartaric acid ethylene diamine.
A piezoelectric device, as a vibration generating device, generates vibrations using mechanical deformation or mechanical stress generated in response to voltage applied thereto.
In order to amplify the mechanical deformation or mechanical stress generated in such piezoelectric devices, a plurality of thin film piezoelectric layers, in which internal electrodes are formed, may be stacked, to produce stronger vibrations.
That is, in piezoelectric devices manufactured by stacking a plurality of thin film piezoelectric layers in which internal electrodes are formed, an electrical field is formed between two electrodes in response to an applied voltage so that mechanical deformation of the structure is caused by dipoles generated in the piezoelectric layers.
By doing so, mechanical strain may result from the deformation in the structure, thereby generating vibrations.
Since the strain of the piezoelectric device increases proportionally to an applied electrical field, a higher amount of voltage is to be applied between electrodes in order to obtain a higher degree of strain.
Since such a higher operating voltage may cause serious problems in a circuit, a piezoelectric device may instead be manufactured such that a plurality of piezoelectric layers are stacked on one another to reduce thickness between the electrodes and thus a larger electrical field may be applied under the conditions of the same voltage, thereby obtaining a higher degree of mechanical deformation.
For instance, if the same amount of voltage is applied to a piezoelectric device having a single layer and to a piezoelectric device having a plurality of layers, a higher degree of strain may be obtained in the latter, as compared to the former.
In multilayered piezoelectric devices, internal electrodes formed in the piezoelectric layers having opposite polarities are alternately stacked on one another in the stacking direction.
To this end, for example, internal electrodes to which a positive voltage is applied are printed such that they are left-sided in the piezoelectric layers to create space, and internal electrodes to which a negative voltage is applied are printed such that they are right-sided in the piezoelectric layers to create space, then the layers are stacked, pressed and fired, and then via holes are formed in the space portion so as to be electrically connected to piezoelectric layers having opposite polarities.
That is, since internal electrodes having opposite polarities are stacked such that they are staggered, the space, in which via holes to electrically connect the internal electrodes to the outside are formed, remains as an inactive region.
Such an inactive region causes the performance of a piezoelectric device to deteriorate when an electrical field is applied to the piezoelectric device to generate strain.
Accordingly, a method for minimizing an inactive region of a piezoelectric device is required.
Patent Document 1 below relates to a piezoelectric actuator for driving a haptic device.
Specifically, Patent Document 1 discloses a piezoelectric actuator for driving a haptic device that includes a piezoelectric body in which a plurality of piezoelectric layers having the same poling direction are stacked; and electrode patterns formed on the piezoelectric body, wherein the length of each of the piezoelectric layers is four times that of the width of the piezoelectric layers or more, and the width of the piezoelectric layers is ten times the thickness of the piezoelectric layers or more.
However, in the piezoelectric actuator disclosed in Patent Document 1, external electrodes are formed on one side of the piezoelectric actuator so that elements corresponding to the conductive vias and insulating vias disclosed in the present invention are not discussed, and thus the feature of minimizing an inactive region of the piezoelectric device is not disclosed.